In recent years, accompanying the development of optical interconnecting techniques, there is demand for the realization of integrated optical transceivers that are suitable for cost reduction. As a technique of realizing such integrated optical transceivers, silicon (Si) photonics is drawing attention. For example, an external resonator laser is proposed that has a configuration in which a light emission element of a III-V compound semiconductor is formed on a silicon substrate so as to control oscillation modes by using a silicon waveguide filter.
FIG. 1 and FIG. 2 illustrate examples of external resonator lasers. In the configuration illustrated in FIG. 1, oscillation occurs between a pair of reflectors Rb and Rf. In the configuration illustrated in FIG. 2, light output from the Semiconductor Optical Amplifier (SOA) to the silicon waveguide returns to the SOA via ring resonators R1 and R2. The light returned from the silicon waveguide is reflected by the reflector Rb and is output to the silicon waveguide again. This causes oscillation. The wavelength of generated laser light is determined by the resonation wavelength of the ring resonators R1 and R2 in the external resonator lasers illustrated in FIG. 1 and FIG. 2.
The configuration illustrated in FIG. 1 is described in for example Japanese Laid-open Patent Publication No. 2006-245344. The configuration illustrated in FIG. 2 is described in for example Japanese Laid-open Patent Publication No. 2009-200091. Further, another related technique is described in Japanese Laid-open Patent Publication No. 2008-34657.
In the configurations illustrated in FIG. 1 and FIG. 2, in order to meet the conditions for the single oscillation mode, it is necessary to accurately control the resonation wavelength of the ring resonators R1 and R2 having different diameters. Accordingly, when the wavelength of the ring resonators shifts due to temperature change or the like, there is a possibility that the oscillation characteristics deteriorate.
Laser light is emitted from the SOAs in the configurations illustrated in FIG. 1 and FIG. 2. Accordingly, when for example the laser light is to be supplied to a device on a semiconductor substrate, optical axis alignment has to be performed, which is troublesome.
In the configuration illustrated in FIG. 1, it may be possible to obtain laser light on the semiconductor substrate by for example implementing the reflector Rf by using a half mirror. In such a case, however, output laser light is under influence of losses occurring in the ring resonators R1 and R2. Accordingly, it is difficult to generate high-power laser light efficiently in this configuration.